Method and apparatus for the biochemical purification of a liquid medium

ABSTRACT

A method and apparatus for the biochemical purification of a contaminated liquid medium, in which the liquid medium is passed through granular filter material provided in a holder and in which the granular filter material (12) contained in the holder is set in motion, preferably with the aid of an injected gas such as air. Microorganisms and/or an active water for microorganisms can be added to the holder. The filter material may comprise a mixture of lava and sand, for example 28% to 38% sand and 61% to 71% lava. The granule size of the sand is 0.3 to 1.2 mm and the granule size of the lava is 2 to 10 mm. The main flow of the medium to be purified and the injected gas are oppositely directed. To set the filter material in motion, use is made of an inner tube (33) placed in an outer tube (32), gas being blown through the inner tube under the lower end of the inner tube (31) so that gas and filter material drawn in at the lower end of the tubes and medium are transported upward through the inner tube.

The present invention relates to a method for the biochemicalpurification of a liquid medium containing contaminants, the liquidmedium being passed through a bed provided in a holder and comprising agranular filter material.

Such methods are generally known. In these methods, the liquid medium isgenerally purified because the granular filter material retains and/orabsorbs contaminants and lets the liquid medium through.

The object of the present invention is to provide an improved method andapparatus of the abovementioned type.

According to the invention, this object is achieved in that the granularfilter material contained in the holder is set in motion. In thisconnection, the granular filter material is preferably set in motion bythe injection of a gas, such as air. On the granular material thereforms a layer, generally a slimy layer, containing bacteria and/ormicroorganisms which absorb and/or convert the contaminants, in whichprocess they purify the liquid medium again chemically. Surprisingly,the purifying action of the bacteria and/or microorganisms appears to beconsiderably assisted if the granular material is set in motion. In thisprocess, the purifying action is further stimulated by using a suitablegas for setting in motion. Such a suitable gas may in many cases be air.The sitting up of the bed is counteracted by the granular filtermaterial being circulated.

According to the invention, it may be advantageous for the furtherimprovement of the purifying action if microorganisms and/or anactivator for microorganisms are/is fed to the holder. Use can also bemade of microorganisms which are already present in the medium and/or onthe filter material. Furthermore, known further purifying agents for,for example, aqueous systems, as well as nutrients for themicroorganisms can be added, as is generally known to persons skilled inthe art. Instead of, or in addition to, microorganisms, bacteria and/oran activator for bacteria may also be supplied.

According to the invention, the support function of the filter materialfor microorganisms and/or bacteria can be appreciably improved if thefilter material comprises porous granules in which the microorganismsand/or bacteria are able to lodge. The more porous the granules, thegreater is the contact surface of the medium to be purified with thebacteria and/or microorganisms.

All the known filter materials for biological filters, such as, inparticular, porous granules, may be used. These materials may optionallybe formed into granules having the desired size before use. Filtermaterials and purifying agents provided on granular support materialsmay also be used.

A BWC (Bio Water Clean), such as the BRC (Bio Reactor Clean) relatedthereto, may be used as activator.

A typical composition for Bio Water Clean is:

dry matter: 95 g/l

moisture content: 905 g/l

organic matter: 50 g/l

inorganic matter: 45 g/l

Organic matter

protein: 7%

carbohydrates: 45%

alginic acid: 24.5%

mannitol: 3.7%

miscellaneous: 16.8%

Growth-stimulating agents

adenine (cytokinin): 0.02%

IAA: 0.03%

ABA: 0.01%

Inorzanic matter (ash)

essential constituents: essential trace elements

(macro-nutrients) (micro-nutrients)

Total nitrogen (N)1.5%

phosphorus (P)0.05%

potassium (K)2.5%

calcium (Ca)1.2%

sulphur (S)3.7%

copper (Cu) 5 ppm

iron (Fe)1200 ppm

manganese (Mn)12 ppm

zinc (Zn)100 ppm

boron (B)80 ppm

molybdenum (Mo)1 ppm

The elements normally found furthermore also comprise: aluminium,antimony, barium, bromine, cadmium, chlorine, chromium, cobalt,fluorine, iodine, lead, mercury, nickel, selenium, silicon, sodium,strontium, tin, tungsten and vanadium.

If Bio Water Clean is used with the filter according to the application,the following advantages are obtained if the filtration water isrecirculated to the glasshouse for watering plants:

better taste, shelf life and quality of the plants and/or cultivatedproducts;

better absorption of metal ions, such as Na⁺, K⁺, Mg⁺, by the plants.

This makes it possible to use, for example, tap water and/or ditch waterin the watering of glasshouses without undesirable build-up of salts inthe recirculation system, for example in the mats on which the plantsare cultivated.

According to the invention, it is advantageous, in particular, if thefilter material comprises fairly large, preferably porous, granules andfairly small granules. The fairly small granules are then able to fillup the gaps between the fairly large granules so that the contactbetween the granules and the filter material is improved.

According to the invention, a very suitable filter material comprises amixture of lava and sand. Such a mixture is preferably composed of 28%to 38% sand and 61% to 71% lava. A so-called filtering sand, forexample, can be used as sand.

Sand having a granule size of 0.3 mm to 1.2 mm, preferably 0.5 mm to 1mm and lava having a granule size of 2 mm to 10 mm, preferably 4 mm to 8mm, appear to give very good results, in particular if these granulesizes are used in combination. Sand and lava having such granule sizescan readily be set in motion and form good supports for microorganismsand bacteria, with a sufficiently large total contact surface. Underthese circumstances, the spaces between the fairly large lava granulesare filled by the fairly small sand granules, as a result of which thecontact of the medium to be purified with the lava granules, andtherefore with the bacteria and/or microorganisms supported therebyand/or therein, is improved.

According to the invention, a very good purifying action is obtained ifcontaminated liquid medium is supplied at the top of the filtermaterial, purified liquid medium is removed at the bottom of the filtermaterial and the filter material is kept in motion by injecting a gas,such as air, into the filter material essentially in a vertical upwardsdirection. Under these circumstances, the contaminated liquid medium isforced from the top downwards through the filter material, while thefilter material itself is set in motion by utilizing the buoyancy of thegas bubbles, with the result that a circulation of filter materialoccurs in the bed.

According to a further advantageous method according to the invention,liquid medium is also forced upwards by the injected gas together withthe filter material. In this case, the purifying action is improvedbecause the liquid medium to be purified is also circulated through theholder. The recirculation of the liquid medium to be purified and filtermaterial takes place, according to the invention, in a very advantageousway because the gas is injected at the lower end of a tube placedessentially vertically in the bed containing filter material andprojecting above it. As a result of arranging for the liquid medium tobe purified, filter material and gas to circulate in such a way, via atube, the liquid medium to be purified is brought into intimate contactwith bacteria and microorganisms which are supported by the granules andwhich can in turn be additionally activated again by the injected gas,for example as a result of the provision of oxygen.

The invention furthermore relates to an apparatus for carrying out themethod according to the invention. Such an apparatus comprises a holderwith supply means for contaminated liquid medium, removal means forpurified liquid medium and means for setting in motion granular filtermaterial to be provided in the holder. Preferably, a granular filtermaterial having a granule size of less than 20 mm is provided in theholder. Granules having such a size, such as porous lava granules, canreadily be set in motion, form a good support for microorganisms andbacteria and form a good contact surface between, on the one hand, themicroorganisms and/or bacteria and, on the other hand, the liquid mediumto be purified.

The means for removing the purified liquid medium advantageouslycomprise a drainage tube or system of drainage tubes provided at thebase of the holder. Such drainage tubes are generally known and can beprovided, for example, on the base of the holder and remove purifiedliquid medium without entraining the granular filter material.

The means for setting the granular filter material in motion preferablycomprise at least one nozzle for injecting a gas, the nozzle beingprovided at a height in the holder which is such that it will besituated in the bed containing filter material to be provided in theholder. In this connection, the nozzle is preferably provided in such away that the gas stream to be injected is directed essentially upwards.

The medium may be any liquid containing impurities, such as aqueousdrainage and feed flows of fabrication processes, market gardens andfarms, and the like. Further applications of the method and apparatusaccording to the invention will be clear to those skilled in the art.

The invention will be explained in greater detail below with referenceto an example of an embodiment shown in a drawing. In the drawing:

FIG. 1 shows a diagram of a system in which a purifying apparatusaccording to the invention is incorporated;

FIG. 2 shows a unit for setting the filter material in motion;

FIG. 3 shows a plan view of an apparatus according to the invention forthe biochemical purification of a liquid; and

FIG. 4 shows a cross section through the apparatus according to FIG. 3.

FIG. 1 shows a purification system for liquids comprising three holders,viz. 1, 2 and 3. Holder 1 is the reaction vessel in which thebiochemical purification of the liquid takes place, holder 2 is a feedbuffer containing liquid to be purified, and holder 3 is a removalbuffer containing purified liquid. It will be clear that the feed buffer2 and the removal buffer 3 may be connected, respectively, to feed pipesand drainage pipes which are not shown. Liquid to be purified is fedfrom the feed buffer 2 to the reaction vessel 1 with the aid of a pumpapparatus 4 via a pipe 5, the pipe 5 discharging into said reactionvessel 1 at the top. Feed buffer 2 is furthermore provided with anoverflow pipe 6, via which contaminated liquid 7 can be removed if thefeed buffer 2 becomes too full.

Microorganisms, bacteria or activators for microorganisms and/orbacteria can be fed to the reaction vessel 1 by means of a dispensingunit 8 connected to the feed pipe 5.

A drain 15 for purification purposes, to be described below, isconnected to the reaction vessel 1, which removal pipe 15 dischargesinto a collecting tank 19. Air-injection means 10 are connected via adistributor 11 having two feed pipes 13 and 14 for air, by means ofwhich pipes air can be injected into the reaction vessel 1 in order toset the filter material 12 in motion. The reaction vessel 1 isfurthermore provided with a level switch 18 which emits a signal if thelevel of the liquid 27 in the reaction vessel 1 reaches a certainheight.

Depending on the setting of the stopcocks 55, 56, 57 and 58, liquid isremoved from the reaction vessel 1 via a pipe system 61 to thecollecting tank 19 or the collecting tank 54. In this connection, theliquid can be removed to collecting tank 19 if the liquid isinsufficiently purified, for example when the installation is started upor restarted. From the collecting tank 19, the liquid can then be fedback to the feed buffer 2 via pipe 21 by means of a pump 20.

If the liquid is sufficiently purified, it can be fed to collecting tank54 from the reaction vessel. The purified liquid can then be removedfrom collecting tank 54 to the removal buffer 3 by means of a pump 53via a pipe 16 and a flowmeter 17. In this connection, the flowmeter 17may be a flowrate meter and/or a cumulative meter which counts the totalamount of liquid conveyed with time.

Pipe section 62 of the pipe system 61 extends essentially horizontallyat a level which is higher than the top of the bed filter material inthe reaction vessel 1. This achieves the result that the liquid level ofthe liquid present in the reaction vessel 1 is always sufficiently highfor the bed to be covered by liquid and not able to dry out.

The removal buffer 3 is provided with a level switch 22 which is able toemit a signal if the level of the purified liquid reaches or exceeds acertain value.

The purification system can be regulated with the aid of the controlunit 9. For this purpose, the control unit 9 is connected via a signalline 23 to the pump 4 in the feedstock buffer, via a signal line 26 tothe compressor means, via signal line 24 to the level switch 22 in theremoval buffer, and via signal line 25 to the level switch 18 in thereaction vessel. It will be clear that the control unit 9 can beconnected via further signal paths which are not shown to, for example,the dispensing unit 8, the distributor 11, the flowmeter 17, or one ormore of the valves, or control valves, which can be shut off.

The operation of the purification system per se shown in FIG. 1 will beclear to a person skilled in the art. The operation of the reactionvessel 1 will now be dealt with in greater detail below.

FIG. 2 shows a detailed view of a section of the reaction vessel 1.

The reaction vessel 1 contains a bed of a granular filter material whichis composed of a mixture of approximately 33% sand and 66% lava. Thegranule size of the sand, preferably filter sand, is approximately 0.5to 1 mm and the granule size of the porous lava is approximately 4 to 8mm. The sand granules will therefore fill up the spaces between the lavagranules, as a result of which the contact between the liquid and thelava granules is improved.

As can be seen in FIG. 2, the level 50 of the liquid 27 is higher thanthe level 51 of the filter material 12, with the result that the saidfilter material does not dry out.

Provided in the reaction vessel is a circulation unit. Said circulationunit comprises an inner tube 33 and an outer tube 32. The inner tube 33is secured centrally in the outer tube 32 by means of a centring device35. The outer tube 32 is attached in turn to a support 30 which may bemounted, for example, on the base of the reaction vessel. Attached tothe support 30 by means of a support arm 34 is a nozzle 31 connected toa feed pipe 13 for air. Said nozzle 31 is situated below the inner tube33 and is directed in such a way that the gas flowing out of it is blownessentially into the inner tube 33.

Provided at the top of the circulation unit is a lid 70. Said lid 70 isprovided with an opening through which the inner tube 33 projects, andsaid lid 70 furthermore fits over the outer tube 32. The space formedbetween the inner tube 33 and the outer tube 32 is thus essentiallyclosed off at the top, and the inner tube 33 is centred in the outertube 32 by the lid 70. This lid construction 70 appreciably simplifiesany maintenance operations on the circulation unit. After all, the lid70 is accessible from the top, with the result that it can be removed,after which the inner tube 33 can also be removed from the outer tube32. The nozzle 31 can then be inspected and, if necessary, cleaned viathe outer tube 32. It will be clear that the filter material does notneed to be removed from the holder during this process, which offersgreat practical advantages.

As can furthermore be seen in FIG. 2, the top end of the inner tube 33is situated above the level 51 of the filter material 12 and higher thanthe top end of the outer tube 32. The top end of the outer tube 32 is,according to FIG. 2, approximately at the same height as the level 51 ofthe filter material 12, with the result that the lid 70 remains readilyaccessible. The top end of the outer tube 32 may, however, also behigher than said level 51 of the filter material 12.

A flow of filter material, air and liquid indicated by the arrows isgenerated as a consequence of the air injected into the inner tube 33 atthe injection point via the nozzle 31. As a result of the action of theinjected air, liquid and filter material are drawn in at the bottom endof the circulation unit and transported upwards through the inner tube.Because the inner tube 33 projects above the filter bed, the filtermaterial fed upwards will spread over the bed as indicated. The liquiddrawn in at the bottom end of the circulation unit has already beenpassed through the bed and has already been to some extent purifiedthereby. Because the liquid is fed upwards again, it has to be fedthrough the bed again, which benefits the purifying action.

During the transport through the inner tube, an intimate contact isbrought about between the granular filter material, the liquid to bepurified and the injected gas, for example air. Said intimate contact isextremely beneficial for the purification of the contaminated liquid.The purified liquid is, as stated earlier, removed by means of drainagepipes provided at the bottom of the reaction vessel, with the resultthat said liquid is transported completely through the layer of filtermaterial 12 from top to bottom, the circulation via the circulation unitensuring that this takes place several times.

The cross-sectional dimensions of the outer tube 32 are such that, atleast at the bottom end of the inner tube 33, a chamber 71 is providedaround said bottom end. In the example shown in FIG. 2, said chamber 71extends around the entire inner tube. Said chamber is open at thebottom. In said chamber, a swirling of granules of the filter materialwhich whirl up and fall back again is generated by means of the airinjected via the nozzle 31. Said air will therefore gradually be fedinto the swirling chamber 71 as well as into the inner tube. Thegranules falling back out of the swirling chamber 71 will fall onto thefilter material present underneath the bottom end of the circulationunit and set said filter material in motion as a result, the supply offilter material to the inner tube 33 thereby being improved. Thiscounteracts the possibility that a space without filter material formsbeneath the bottom end of the circulation unit.

To counteract an accumulation of air in the swirling chamber, ventingopenings, which are not shown, are provided. Said venting openings maybe provided, for example, at the top of the circulation unit in the wallof the inner tube 33, with the result that a connection is provided atthis point between the swirling chamber and the interior of the innertube.

FIGS. 3 and 4 show, respectively, a plan view and a cross section of areaction vessel according to the invention. As can be seen from thesefigures, the removal pipe 16 for purified liquid is connected to adrainage system 36 which is provided spirally at the base of thereaction vessel. Furthermore, it can be seen in these figures that thepipe 14 for supplying a gas, such as air, discharges into a pipe system37 likewise provided spirally at the base of the reaction vessel. Saidpipe system, such as, for example, a perforated tube, is provided with amultiplicity of nozzles in order to be able to inject additional gasinto the filter material. Said additional gas can be used in order toset the filter material additionally in motion, at the same time assetting in motion by means of the circulation unit. But said pipe system37 can also be used for setting the filter material very vigorously inmotion at set times so that dirt present in the filter material is blownupwards and can be removed via the funnels 38 which are connected to theremoval pipe 15. In this case, the filter material present in thereaction vessel is itself then subjected, therefore, to a purificationtreatment at set times.

In FIGS. 3 and 4, it can furthermore be seen that a multiplicity ofcirculation units are provided in the reaction vessel, and specifically,four circulation units. It will, however, be clear that, depending onthe size of the reaction vessel, a greater or lesser number ofcirculation units may be provided. Said circulation units are preferablyprovided in a regular pattern. Thus, the circulation units may bedistributed at regular angular distances over a circle, as is the casein FIG. 3. However, a plurality of such circles containing circulationunits may be provided in the reaction vessel. It may furthermore be veryadvantageous to provide a further circulation unit in the centre of thereaction vessel, but this is not shown in FIG. 3 since this would notbenefit the clarity of the figure.

It will be clear that many variants falling within the scope of theinvention are conceivable in relation to the exemplary embodiment of theinvention described above.

The method and apparatus according to the invention can be veryadvantageously used for purifying irrigation water collected in thecultivation of plants in glasshouses, after which the purifiedirrigation water can be reused for irrigation.

The use of the method according to the application will now be explainedby reference to the following, nonrestrictive examples.

EXAMPLE 1

Drainage water from a glasshouse was filtered with the filter accordingto the application using Bio Water Clean. The aerobic microbial countand the amount of fungi were determined upstream and downstream of thefilter. The results were as follows:

    ______________________________________                                        Analytical result of microbiological examination                              of drainage water                                                                              I     II                                                     ______________________________________                                        aerobic microbial count/ml                                                                       500,000 70,000                                             fungi/ml           100     <10                                                ______________________________________                                         I: upstream of filter                                                         II: downstream of filter                                                 

This reveals the appreciable biological purification which is obtainedby the method according to the invention.

EXAMPLE 2

Plant sap analyses

To determine the effect of the method according to the invention, a testwas carried out in which, in one holding, a normal cultivation was useduntil 1 Jun. 1994, while, in another holding, the invention was usedfrom 1 Apr. 1994, Bio Water Clean being given along with the feedsolution.

The differences between the two test projects were determined, interalia, on the basis of analyses carried out weekly on plant saporiginating from young, fully grown leaf. The most important chemicaldata follow below.

    __________________________________________________________________________    27/04/94 04/05/94                                                                           11/05/94                                                                           19/05/94                                                                           26/05/94                                                                           02/06/94                                                                           08/06/94                                                                           16/06/94                               __________________________________________________________________________    Untreated until 1 June 1994                                                   EC  17.0 14.1 13.6 15.8 14.8 12.4 12.0 11.9                                   pH  6.3  6.3  6.4  6.5  6.3  6.2  6.1  6.4                                    K   6.34 5.46 4.88 5.98 5.49 4.69 4.58 3.99                                       7.0  2.0  1.0  9.0  6.0  3.0  4.0  6.0                                    Ca  946.0                                                                              887.0                                                                              1.07 1.13 1.32 1.35 1.28 1.29                                                 8.0  9.0  0.0  2.0  9.0  1.0                                    Mg  311.0                                                                              253.0                                                                              254.0                                                                              231.0                                                                              272.0                                                                              257.0                                                                              304.0                                                                              364.0                                  Na  289.0                                                                              230.0                                                                              262.0                                                                              249.0                                                                              327.0                                                                              204.0                                                                              205.0                                                                              222.0                                  NO.sub.3                                                                          1.79 1.50 1.61 1.85 1.60 1.29 1.33 887.0                                      2.0  4.0  6.0  9.0  7.0  6.0  3.0                                         Si  31.4 18.7 40.6 39.4 38.3 37.7 33.3 34.1                                   Treated from 1 April 1994 onwards                                             EC  16.7 13.7 15.1 14.9 12.8 11.3 10.6 11.2                                   pH  6.3  6.4  6.3  6.3  6.1  6.1  6.0  6.1                                    K   6.08 5.31 5.73 5.58 4.62 4.57 4.26 3.85                                       5.0  7.0  5.0  5.0  6.0  2.0  2.0  8.0                                    Ca  1.36 1.41 1.55 2.06 1.76 1.98 1.93 1.64                                       9.0  6.0  0.0  8.0  1.0  1.0  0.0  8.0                                    Mg  403.0                                                                              358.0                                                                              421.0                                                                              464.0                                                                              381.0                                                                              397.0                                                                              419.0                                                                              448.0                                  Na  349.0                                                                              287.0                                                                              363.0                                                                              397.0                                                                              297.0                                                                              201.0                                                                              198.0                                                                              191.0                                  NO.sub.3                                                                          1.68 1.43 1.90 1.59 1.11 873.0                                                                              779.0                                                                              688.0                                      4.0  5.03 7.0  8.0  5.0                                                   Si  31.4 34.0 44.1 51.9 46.6 45.1 52.3 38.2                                   __________________________________________________________________________

The fact that the crop was more vigorous and healthier in the case ofthe treated site was also clearly evident from the analytical figures.In particular, the Ca content is sometimes 40-50% higher. This revealsthat the Ca transport from root tops to plant parts, which fairlyfrequently presents problems, functions well here. As is known, calciumis used in the plant for building up cell walls and membranes. In meloncultivation, this is manifested in a sturdier fruit with a longer shelflife. Further advantages are:

Advances in terms of production on the previous year despite the dullerspring.

Greater production, certainly in kilograms. An increase in production ofmore than 10% is among the possibilities.

The average piece weight is markedly higher. The grades 5 and 6 areharvested per box, with an average piece weight of 1500 or 1200 grams,respectively.

The crop is more vigorous and less sensitive to disease and stress,particularly to Pythium, Mycosphaerella, etc., and produces more leaf.

The sugar content of the melons is on average 1.5% higher (now 11-12%).

As a result of the sturdier cell structure, the fruits keep for stilllonger.

I claim:
 1. In a method for the biochemical purification of a liquidmedium containing impurities, wherein the liquid medium is passedthrough a bed containing granular filter material provided in a holder,wherein contaminated liquid medium is supplied at the top of the filtermaterial, wherein purified liquid medium is removed at the bottom of thefilter material, wherein a tube is placed essentially vertically in thebed containing filter material and projects above the latter, wherein atleast at the bottom end of the tube a chamber is provided around thebottom end of the tube, the chamber being open at its bottom, whereinnear the bottom end of the tube a gas is injected such that as aconsequence of the ejector action of the injected gas filter materialand medium are drawn in from the surrounding of the bottom end of thetube, that the injected gas feeds said filter material and medium drawnin upwards via the tube, and that the filter material fed upwards isspread over the bed; the improvement wherein the gas is injectedessentially in a vertically upwards direction from below the bottom endof the tube such that the gas is blown into the tube for feeding upwardfilter material and medium and blown into the chamber such that aswirling of bottom material whirling up and falling back again isbrought about in said chamber with the result that bottom materialfalling back sets the bottom material around the bottom end of the tubein motion.
 2. Method according to claim 1, wherein microorganisms and/oran activator for microorganisms are/is fed to the holder.
 3. Methodaccording to claim 1 wherein the filter material contains porousgranules.
 4. Method according to claim 1, wherein the filter materialcomprises large and small granules.
 5. Method according to claim 1,wherein the filter material comprises a mixture of lava and sand. 6.Method according to claim 5, wherein the sand has a granule size of 0.3mm to 1.2 mm.
 7. Method according to claim 5, wherein the lava has agranule size of 2 mm to 10 mm.
 8. Method according to claim 1 whereinthe filter material comprises 28% to 38% sand and 61% to 71% lava.
 9. Ina device for the biochemical purification of a liquid medium containingcontaminants, comprising a holder (1) with feed means (5) forcontaminated liquid medium, removal means (61) for purified liquidmedium and means (31, 33) for setting granular filter material (12) tobe provided as a bed in the holder (1) in motion, wherein said means forsetting the filter material in motion comprise an essentially verticaltube and at least one nozzle for injecting a gas, in which the tube issituated in the holder such that it will be situated in the bedcontaining filter material to be provided in the holder, the top end ofthe tube being higher than the top of the filter bed to be provided inthe holder, and in which the nozzle is provided near the lower end ofthe tube; the improvement wherein a chamber open at the bottom is formedaround the lower end of the tube, and the at least one injection nozzleis directed essentially upwards to blow gas into the tube and into thechamber.
 10. Device according to claim 9, wherein a bed of granularfilter material having a granule size of less than 20 mm is provided inthe holder.
 11. Device according to claim 9, wherein the granular filtermaterial comprises porous granules.
 12. Device according to claim 9,wherein the granular filter material comprises a mixture of lava andsand, containing 28% to 38% sand and 61% to 71% lava.
 13. Deviceaccording to claim 12, wherein the granule size of the sand is 0.3 mm to1.2 mm.
 14. Device according to claim 12, wherein the granule size ofthe lava is 2 mm to 10 mm.
 15. Device according to claim 12, wherein thegranule size of the sand is 0.5 mm to 1 mm.
 16. Device according toclaim 12, wherein the granule size of the lava is 4 mm to 8 mm. 17.Device according to claim 9, wherein the removal means for the purifiedliquid medium comprise a drainage tube provided at the base of theholder.
 18. Device according to claim 9, wherein the feed meansdischarge in the holder above the filter material to be provided in theholder.
 19. Device according to claim 9, wherein the section of thevertical tube (33) situated in the bed is placed in a casing (32) andwherein a free space (71) which is open at the bottom is present betweenthe casing (32) and the vertical tube (33).
 20. Device according toclaim 9, wherein the holder is provided with a multiplicity of verticaltubes which are distributed evenly over the holder and have nozzlesprovided at the bottom.